Ok, I figured something out! Yay, data is helpful!
So, in order for youngest kid to not lose her medi-cal benefits, we cannot make more than 266% of FPL (fed. poverty level) - if I were to take the job for the required number of hours, we would go above that figure.
Even if we make right up to that limit, we will remain in the same tax bracket we're currently in, though as we make more, my insurance premiums will increase. My assessment (pending lhamo's input based on her experience) of the FEIE (foreign earned income exclusion) suggests that we'll get to claim it next year, even if DH returns home again this year, as he will, to attend youngest kid's HS graduation.
I like my boss - we've known each other for a number of years and I consider her a friend and there's an easy camaraderie between us. If I had my 'druthers' though, I still wouldn't work 40hrs/week at the cafe. I like being able to go home and leave it all behind and I like having the balance between active/sociable work and the brain-work of my editing with a bit of time on the side for my own random projects.
So, there are a few reasons for me to not up my hours and responsibilities.